One of the experimental facilities at the German laboratory

GSI Helmholtz Centre for Heavy Ion Research The GSI Helmholtz Centre for Heavy Ion Research (german: GSI Helmholtzzentrum für Schwerionenforschung) is a federally and state co-funded heavy ion () research center in the Wixhausen suburb of Darmstadt, Germany. It was founded in 1969 as th ...

Darmstadt Darmstadt () is a city in the state of Hesse in Germany, located in the southern part of the Rhine-Main-Area (Frankfurt Metropolitan Region). Darmstadt has around 160,000 inhabitants, making it the fourth largest city in the state of Hesse ...

is an Experimental Storage Ring (ESR) with

electron cooling Electron cooling is a method to shrink the emittance (size, divergence, and energy spread) of a charged particle beam without removing particles from the beam. Since the number of particles remains unchanged and the space coordinates and their der ...

in which large numbers of highly charged

radioactive Radioactive decay (also known as nuclear decay, radioactivity, radioactive disintegration, or nuclear disintegration) is the process by which an unstable atomic nucleus loses energy by radiation. A material containing unstable nuclei is consi ...

ions can be stored for extended periods of time. This facility provides the means to make precise measurements of their decay modes. The absence of most or all of the

electron The electron ( or ) is a subatomic particle with a negative one elementary electric charge. Electrons belong to the first generation of the lepton particle family, and are generally thought to be elementary particles because they have n ...

s in the ions simplifies theoretical treatments of their influence on the decay. Also, such a high degree of ionization is typical in stellar environments where such decays play an important role in

nucleosynthesis Nucleosynthesis is the process that creates new atomic nuclei from pre-existing nucleons (protons and neutrons) and nuclei. According to current theories, the first nuclei were formed a few minutes after the Big Bang, through nuclear reactions in ...

. In 2007 an ESR experiment reported the observation of unexpected

modulation In electronics and telecommunications, modulation is the process of varying one or more properties of a periodic waveform, called the '' carrier signal'', with a separate signal called the ''modulation signal'' that typically contains informat ...

in time of the rate of

electron capture Electron capture (K-electron capture, also K-capture, or L-electron capture, L-capture) is a process in which the proton-rich nucleus of an electrically neutral atom absorbs an inner atomic electron, usually from the K or L electron shells. ...

decays of highly ionized heavy

atom Every atom is composed of a nucleus and one or more electrons bound to the nucleus. The nucleus is made of one or more protons and a number of neutrons. Only the most common variety of hydrogen has no neutrons. Every solid, liquid, gas, a ...

s — ¹⁴⁰ Pr⁵⁸⁺, which have a lifetime of 3.39 min. Such findings were soon repeated by the same group, and were extended to include the decay of ¹⁴² Pm⁶⁰⁺ (lifetime 40.5 s). The oscillations in decay rate had time periods near to 7 s and amplitudes of about 20%. Such a phenomenon had not been previously observed, and was difficult to understand. The experimental group considered it very improbable that the appearance of the phenomenon is due to a technical artefact because they report that their detection technique provides—during the whole observation time—complete and uninterrupted information upon the status of each stored ion. As this type of

weak Weak may refer to: Songs * "Weak" (AJR song), 2016 * "Weak" (Melanie C song), 2011 * "Weak" (SWV song), 1993 * "Weak" (Skunk Anansie song), 1995 * "Weak", a song by Seether from '' Seether: 2002-2013'' Television episodes * "Weak" (''Fear t ...

decay involves the production of an

electron neutrino The electron neutrino () is an elementary particle which has zero electric charge and a spin of . Together with the electron, it forms the first generation of leptons, hence the name electron neutrino. It was first hypothesized by Wolfgang Pauli ...

, attempts at the time were made to relate the observed oscillations to neutrino oscillations, but this proposal was highly controversial. In 2013, a similar experimental group at the ESR now called the Two-Body-Weak-Decays Collaboration reported further observations of the phenomenon with measurements on ¹⁴²Pm⁶⁰⁺ with much higher precision in period and amplitude. The same period was observed, but the amplitude was only about a half of that previously seen. Moreover, a follow up high-statistics study (2019) did not observe any time modulation: indicating the observed anomaly was purely statistical, with no physical origin.

References

* *{{cite web , url=http://web.mit.edu/redingtn/www/netadv/XperDecRat.html , title=The Net Advance of Physics: VARIABILITY OF NUCLEAR DECAY RATES maintains a collection of research papers on the GSI K-Capture Anomaly Nuclear physics Experimental particle physics